Flares from the Tidal Disruption of Stars by Massive Black Holes

Abstract

Tidal disruption flares are differentiated into two classes -- those which are sub-Eddington and those which radiate near the Eddington limit. Flares from black holes above ~2 x 10^7 M_\odot will generally not radiate above the Eddington limit. For a Schwarzschild black hole, the maximum bolometric luminosity of a tidal disruption is ~L_Edd(5 x 10^7 M_\odot), substantially below the Eddington luminosities of the most massive disrupting black holes (~2 x 10^8 M_\odot). Bolometric corrections to the spectra of the brightest flares are found to be large (~7.5 mag). Nevertheless, the brightest flares are likely to have absolute magnitudes in excess of -19 in V and -21 in U (in the absence of reddening). Because the spectra are so blue, K-corrections may actually brighten the flares in optical bands. If such flares are as frequent as believed, they may soon be detected in low or high redshift supernovae searches. The He II ionizing radiation produced in the flares may dominate that which is produced by all other sources in the centers of quiescent galaxies, creating a steady state, highly ionized, fossil nebula with an extent of ~1 kpc which may be observable in recombination lines.